Method for heat recovery

ABSTRACT

A method and an apparatus for the heat recovery from plants in which waste heat is produced at different waste heat sources and fluids are emitted at different temperatures, said method and said apparatus striving after a total optimization of the heat recovery without efficiency losses caused by missing instantaneous compensation between the amount produced waste heat and the need thereof. Said method comprising the steps of collecting waste heat in emitted fluid or fluids at every waste heat source of group of mutually similar waste heat sources and assorting said waste heat with regard to temperatures and as required accumulate it at the highest temperature as possible. Collected heat is then fed back directly or indirectly via the accumulators to the heat requiring unit the temperature need of which is with as low value as possible below the temperature of the feed-back heat. Said apparatus is characterized in that said waste heat sources (M 1  -M 4 ) are in groups connected with heat collecting devices which by temperature controlled change-over devices (O 1 ) are connected with heat accumulators (A 1  -A 3 ), said heat consuming units (M 1 , M 3 , M.sub. 5, LU, TVV), being connected with these by means of change-over devices (O 2 ) in such a way that every heat consumer is connected with the heat source the temperature of which with as low value as possible increases the temperature need in the heat consumer.

The invention is related to a method and an apparatus for heat recoveryin which waste heat is produced at different heat sources andtemperatures, said method and said apparatus being so formed that totaloptimization can be obtained.

In many industries in which energy intensive processes and machines areused, in the paper-, textile- and washing industry for instance,significant amounts of energy are emitted to the environment withexhaust liquids, moisty outlet gases and different cooling mediums.

In such situations in which in order to save energy equipments forenergy recovery are put in, the traditional way is to form thisequipment to be used between emitted and supplied fluids, whereby a heatexchange occurs at a single machine or possibly a group of mutuallysimilar machines.

On thermodynamical principles it follows that heat energy at a hightemperature can be seen as higher "quality" than heat energy at a lowertemperature. The conventional heat recovery often does not either giveany opportunity to supply recovered waste heat to a process step withthe exact high "quality" which is needed. Hereby follows that even ifthe totally recovered energy amount at a machine easily should besufficient, there is in practice no possibility to this, since perhapsthe recovered heat has a too low temperature.

Heat recovery often has the effect that simultaneousness must existregarding the emitting of waste heat and the need thereof. For example,in a machine which has great thermal inertia and which after anoperation stop must be cooled during a proportionately long period, thefree waste heat cannot be re-used if the heat recovery only occurslocally, since any corresponding heat need to the machine does not existafter it has been stopped. Hence, the traditional local heat recoverymeans difficulties to with regard to the time compensate the supply ofwaste heat and the need thereof.

A method to recover heat from exhaust water which is supplied to a heatexchanger is previously known from e.g. SE-PS 382 496. When thetemperature of the supplied exhaust water is below the temperature ofthe exhaust water in the heat exchanger the supplied exhaust water isby-passed the heat exchanger.

This method to recover heat from exhaust water is heat wasting for thereason that a great portion of the heat in the exhaust water isby-passed directly the heat exchanger and is therefore not recovered.

It is an object of this invention to provide a method for the recoveryof heat from a process in which fluids are emitted at differenttemperatures from several waste heat sources, said method being definedto avoid the drawbacks mentioned above, i.e. to obtain a totaloptimization of the heat recovery, and simultaneously to increase theaccessibility for waste heat and the use of the apparatus.

This object is attained according to the invention by the fact that thewaste heat in said fluids is collected from every waste heat source orfrom mutually similar waste heat sources, that collected waste heat isassorted with regard to temperature and is then fed back to the systemand/or a further consumer, said feedback being provided at a temperatureas low as possible with regard to the application thereof.

To compensate varying need of waste heat values, but even varying mediumflows from waste heat sources, collected waste heat values can beaccumulated at the highest possible of a number of predeterminedtemperatures.

At a modified embodiment of the method according to the invention saidcollecting can be achieved by heat exchanging from the fluid of thewaste heat source to a heat carrying fluid.

Another modified embodiment implies a direct discharge of a heatcarrying fluid.

The invention is also related to an apparatus for executing said method,which apparatus comprises a number of waste heat sources with fluidoutlets, especially of different temperatures, said apparatus beingcharacterized by the fact that the fluid outlets dependent on the fluidand the temperature thereof, are to be connected to each other in groupsconnected with a heat collecting device each, said heat collectingdevices being connected with heat consumers included in said system insuch a way that the temperature necessary in said heat consumer with avalue as low as possible is below accessible temperature in the heatcollecting device connected therewith.

A practical embodiment of said apparatus according to the invention isfurther characterized by the fact that it comprises a number of heataccumulators with different temperatures, each heat collecting devicebeing connected with the heat accumulator in which the temperature witha value as low as possible is below the temperature in the heatcollecting device and by the fact that the heat accumulators areconnected with consumers included in said system.

In systems or processes in which temperatures from one and the samemachine can vary in a relatively great temperature interval, a higherefficiency is obtained than in the case that a change-over device isprovided for connection with a certain heat accumulator dependent oninstantaneously existing temperatures.

For a better understanding of this invention reference is made to thefollowing description, taken in connection with the accompanyingdrawings.

FIG. 1 shows a block scheme of the basic principle of the invention.

FIG. 2 shows the invention applied on a washing plant.

FIG. 3 shows the invention applied to a plant for textile fabrication.

FIG. 4 shows the invention applied on the circuit solution of thecentral unit included in the plant of FIG. 3.

FIG. 5 shows the circuit solution for a bleachery and a dye houseincluded in the plant of FIG. 3.

FIG. 6 shows the circuit solution at dressing tenters included in theplant of FIG. 3.

FIG. 7 shows the circuit solution for an air supporting and conditioningunit included in the plant of FIG. 3.

The invention is based on the fundamental idea that waste heat is to beregarded as an energy raw product which is systematically collected froma process and is assorted dependent on temperature and the type of heatcarrying fluid which, possibly after work up, is fed back to the plantin such a way that the quality as close as possible corresponds to therequirements of heat quality in the heat consuming machine. In the basicinventive idea it is also included the requirements of a compensation oftime as well the fluids as the access to and the demand for producedwaste heat which in practice means the occurrence of heat accumulatorswhich have different temperatures. Possibly, there are devices for thesupply of additional heat.

In FIG. 1 as a block diagram the basic principle of the invention isshown. Four units M₁, M₂, M₃ and M₄ represent waste heat sources whichcan exist in a washing, textile or paper pulp industry for instance.Said units can consist of separate process steps or groups of similarmachines. The expression "similar" means, in this connection, thatemitted waste heat is carried of one single medium at approximately thesame temperature.

The units M₁, M₅, M₃, LU and TVV shown to the right in FIG. 1 representheat consumers, said units M₁ and M₃ being able to coincide with theunits shown at the left in FIG. 1 with the same references, while theunit M₅ is a unit which consumes but not produces waste heat. In thesame way the units LU and TVV only consume heat but are not themselvesproducing any heat. The reference LU means local heating and thereference TVV means tapping hot water.

The part within the rectangle indicated by dashed lines can be regardedas a central unit and includes heat accumulators, in the shownembodiment three accumulators A₁, A₂ and A₃, said heat accumulatorsworking at different temperatures. Further, the central unit comprisestwo change-over devices of which the one on the left hand O₁ has as anobject to connect the waste heat sources M₁ -M₄ with the heataccumulators A₁ -A₃ in such a way that the waste heat source isconnected with the accumulator which with as low value as possible isbelow the temperature of the heat emitted from the waste heat source. Inthe corresponding way the other change-over device O₂ has as an objectto connect the heat accumulators A₁ -A₃ with the heat consumers M₁, M₅,M₃, LU and TVV shown in such a way that heat consumers are connectedwith heat accumulators where the temperature with as small value aspossible is below the requested temperature in the heat consumer.

The central unit can also be connected with an outer heat source VK,which supplies the net energy which is not produced by the heatrecovery. Moreover, inlets for admitted fluids are preferably connectedwith the central unit, which inlets are represented by the reference IN.Finally the central unit comprises, as desired, heat exchangerequipments and control equipments.

Regarding the change-over devices O₁ and O₂ it can be said that theypartily can consist of fixed line connections between the units M₁ -M₅and LU and TVV which is of current interest when the units have constanttemperatures with regard to the time at admitted as well as at requiredsupplied heat. In certain situations one or some units work with varyingtemperatures which is exemplified by a washing machine which is workingwith pre-washing, main-washing and rinsing. In such a situationchange-over can be required of the heat emitting unit to different heataccumulators. In a similar way the requirements of temperature at a heatconsumer can vary with regard to the time and an active change-overbetween the different heat accumulators can be required.

In many cases heat carrying mediums emitted from the waste heat sourcecan be led to the central unit, be assorted there dependent on thetemperature and thereafter be supplied to the respective heataccumulator. In other situations the heat carrying medium from the wasteheat sources cannot due to its physical characteristics be storeddirectly in the heat accumulators, and in such cases a heat exchanger isconnected between the waste heat source and the central unit. As anexample a waste heat source can emit heated flows of moist air.

M₁ and M₃ are units which both emit and require heat. If thetemperatures of the emitted and supplied heat fairly correspond to eachother, according to the invention, nothing obstructs that a local heatexchange is provided between the supplied and emitted fluids to theseunits. Possible net energy need is supplied to or emitted from thecentral unit. M₂ and M₄ are units which produce waste heat but have nota heat demand which must be satisfied from the central unit. M₅ is aunit which consumes waste heat from the central unit but does not emitany heat energy in such a way that this heat energy can be taken careof. The same conditions are applicable on the local heating LU and thetapping hot water TVV which even does not supply the central unit withany waste heat.

The most important point has been directed on the static characteristicsof the invention, i.e. the capacity of transferring waste heat from oneor many sources to one or many heat consumers in such a way thattemperatures "as close as possible fit to each other". The use of thecentral unit with the heat accumulators also means that a dynamic systemhas been created, whereby variations on emitted heat amounts and flowsof fluids and required such heat amounts does not any longer mean anydiminishing of the recovery efficiency. By means of the energyaccumulators of the central unit and the connection of the central unitwith an outer heat source no requirements of instantaneouslycompensation between waste heat production and energy consumptionoccurs. Instead, waste heat is taken up in the tact which is required atevery machine or process step. The central unit can be seen as a hubwhich admits waste heat flows and store these flows to thereafterdistribute the waste heat without diminishing the energy recoveryefficiency.

In FIG. 2 a washing plant is shown which comprises three water washingmachines 1. The machines have each an outlet 2 which is connected withthree-way valves 3. From each three-way valve is extending on one handan outlet line 4 which is open out to a final exhaust system 11, and onthe other hand a line 5 which is connected with a collecting line 6which opens to a store tank 7. This tank is via a line 9 which isprovided with a pump 8, connected with one side of a heat exchanger 10.The outlet from this side of the heat exchanger is connected with theexhaust 11. The heat exchanger works with counter-current and is withthe inlet to its other side connected with the cold water inlet 12 ofsaid plant. The outlet from the other side of the heat exchanger is viaa pump 17 connected with the upper part of a bumper tank 16 coupledthereto as a layer accumulator. The bottom of the tank is connected withthe cold water inlet 12, and the inlet of the secondary side of the heatexchanger 10.

In FIG. 2 a hot air exhaust over a mangle is shown. At the reference 18heat is emitted at a relatively low temperature via a line 22 to theupper part of the tank 16. From the lower and cold part of theaccumulator tank 16 water is circulated by means of a pump 23 back tothe heat source 18 for heating and further transporting to the upperpart of the tank.

In the circuit solution shown the heat exchanger 10 and the heat source18 work in a parallel relationship for the charge of the tank 16.

The upper and hot part of the tank 16 is via a line 13 connected withthe washing machines 1. Further, the tank 16 is via a pump 24 and a heatsource 25 connected with the upper end of another accumulator tank 19which also at its hot end has an outlet to a line 20 which via inletlines 21 is connected with the washing machines 1. The lower and coldpart of the tank 19 is via a line 26 connected with the suction side ofthe pump 24 so that the heat source 25 can charge the accumulator tank19 with water of proportionately high temperature.

If the heat changer and the heat source 18 emit heat at a highesttemperature around 40° C., the accumulator tank 16 will gradually befilled up with water at this temperature. This water is then at thedisposal at the inlet to the pump 24, whereafter the temperatureincrease occurs in the heat source 25 so that the operation temperaturein the upper part of the accumulator tank 19 can be at 80° C.

The accumulator tank 19 has an outlet which via the line 20 is connectedwith the washing machines. The lines are via inlet lines 14 and 21,respectively, connected with the shunt valve, by means of which thetemperature in the washing machines 1 can be chosen between thetemperature in the tank 16 and the tank 19. Moreover, the washingmachines 1 have inlets which via the line 27 are connected with the coldwater inlet 12 of the plant so that also the washing machines can besupplied with cold water.

When a washing operation is finished in any of the washing machines 1and the washing water is to be emitted the temperature of the outletwater from the machine is sensed in proportion to the temperature of thewater in the store tank 7. As soon as the temperature of the outletwater with an apt value increases the temperature in the store tank 7the respective valve 3 is set so that the outlet water is emitted to thestoring tank 7 by the lines 5 and 6. If, on the other hand, the outletwater from the washing machine would not have the required temperaturethe respective valve 3 is set in such a way that the outlet water istransferred by the line 4 to the final exhaust 11. When the hot outletwater is driven from the tank 7 through the heat exchanger 10 by meansof the pump 8, heat is transferred from the outlet water to the chargecircuit for the tank 16. Hereby, for instance, the outlet water in thetank 7 can, i.e. the water flowing through one of the circuits of theheat exchanger, have an inlet temperature of 50° C. and an outlettemperature of 20° C. Hereby, at the same flows on both sides of theheat exchanger 10, an increase of the temperature is attained on thewater possibly coming from the cold water inlet 12 for instance from 13°C. to 43° C. being accordingly the approximately final temperature inthe storing tank 16.

In FIG. 3 a plant for heat recovery within textile industry is shown.This plant comprises an air treatment and a conditionary unit 28 whichis provided to make use of air carried heat at low temperature of theorder of 35°-45° C., and to use it to temper the local supply air whichis given a proportionately high relative humidity to diminishing theproblems with static electricity. In this unit an apparatus is includedwhich without heat recovery provides said treatment.

In the plant is further included a number of drying machines from whichair is emitted at about 85° C., said heat being recovered and derivedfor use at another place in the plant.

In connection with the drying unit 29 a dyeing and washing unit 30 isalso placed which, however, in FIG. 3 is separated from the drying unit29. In the dyeing and washing unit 30 waste water is emitted at varyingtemperatures, wherefore an assorting device is comprised which deriveswater on one hand to the outlet and on the other hand to a heat recoverydevice.

The plant comprises also a machine unit 31 with dressing tenters fromwhich heated air is emitted in great flows at about 150° C. In this unitlocal heat exchange occurs between consumed air and fresh air which issupplied from the surrounding environment.

Finally, the plant of FIG. 3 comprises a central unit 32 including twoas layer accumulators coupled bumper tanks working at differenttemperatures, and further two heat exchangers which supply the plant thenet energy which cannot be recovered.

In FIG. 4 a simplified circuit solution within the central unit isshown. The references 33 and 34 denote the bumper tanks which arecoupled as layer accumulators of which the tank 33 works in a lower andthe tank 34 in a upper temperature interval. Vapour heat exchangers 35and 36 are coupled to both the bumper tanks. Said vapour heat exchangers35 and 36 are coupled in parallel relationship between an vapour inlet37 and an outlet 38 for condensate or lower pressure vapour. Further,the central unit has an inlet 39 for cold water which is connected withboth a cold water outlet 40 and an inlet 41 which is connected with thelow temperature end of the layer accumulator 33. The hot end of thelayer accumulator 33 is connected with both an outlet 42 and an inletfor recovered low temperature heat. Finally, the upper end of theaccumulator tank 33 is connected with the lower end of the accumulatortank 34.

The central unit has moreover an inlet 44 for recovered high temperatureheat and a corresponding outlet 45 for the emitting of high temperatureheat. Both these connections are in flow connection with the upper andhottest end of the layer accumulator 34 of FIG. 4. An outlet 47 for hotwater is also coupled in parallel relationship over this accumulator 34by a shunt valve 46, said temperature being in this way able to be setby way of the shunt valve.

The connection of the central unit as described above admits thatrecovered heat in a lower temperature range both can be emitted directlyfrom the central unit and can be used for charging of the loweraccumulator tank 33, whereby this is able dependent on the time tocompensate the supply and the demand on the recovered heat. In the sameway recovered heat in high temperature interval can be used on one handdirectly and on the other hand for charging of the layer accumulator 34,which accordingly provides for a compensation dependent on the time ofthe supply and the need of heat within the upper temperature interval.Further, it is possible to feed the plant with an additional net supplyof heat energy to the plant by means of the heat exchangers 35 and 36.

In FIG. 5 the circuit solution for the drying unit 29 of FIG. 3 isshown. It can be seen that the machine group comprises drying devices48, 49 and 50, which emit flows of heated air at about 85° C. This airis conducted through a filter 51 and through a heat exchanger 52 torecover the heat carried of the air. The outlet 53 of the heat exchanger52 is by means of lines connected with the low temperature inlet 43 ofthe central unit, see FIG. 4, while the inlet of the heat exchanger 52is connected with the cold water outlet 40 of the central unit, see FIG.4.

In FIG. 6 the unit 31 with the dressing tenters is shown. These machineunits have the references 55 and 56. From these machine units greatvolume flows of air heated to a relatively high temperature, about 150°C., are emitted. The heated air emitted from the dressing tenters passesthrough a filter 57, and then through a first heat exchanger 58, andthereafter through a second heat exchanger 59, and is driven of a fan 60to an air outlet which preferably is provided outdoors. Moreover, thismachine unit comprises a fresh air inlet 61 from which air is conductedvia a filter 62 to a heat exchanger 63 and is driven of a fan 64 to theinlet sides of the dressing tenters 55 and 56.

The heat exchanger 58 is coupled so that heat is emitted to the heatexchanger 63, whereby a local heat exchange occurs between emitted andsupplied air flows. Surplus heat from the heat exchangers 58 and 59 isemitted via an outlet 65 to the inlet 44 of the central unit, see FIG.4, for high temperature heat, while the inlet 66 is connected with theoutlet 40 of the central unit for cold water.

In FIG. 7 the circuit solution for the air treatment unit 28 of FIG. 3is shown. This unit comprises hot air producing machines 67, 68, 69 and70, said hot air being emitted at a low temperature, of the order of35°-50° C. The emitted output air includes certain contaminations due towhich this air cannot be used directly as local input air. The sosomewhat contaminated air is driven by two fans 71 and 72 in a scrubberunit 73 in which contaminations are removed simultaneously as therelative humidity in the air is increased strongly. Due to theevaporation of injected water in the scrubber unit heat is consumedwhich firstly is taken from the air stream, whereby the temperaturethereof is lowered. For the treated air to get an apt temperature aslocal supply air additional heat is supplied as desired into a heatexchanger 74 which is connected downstreams of the scrubber unit 73.From the heat exchanger 74 the air then is emitted through an outlet.

Between both fans 71 and 72 are provided an air inlet 76 and an airoutlet 77, whereby a part of the consumed outlet air can be blown outwhile a corresponding volume fresh air is supplied at the suction sideof the fan 72.

Besides the units described above the air treatment unit 28 of FIG. 3comprises a component group, shown in FIG. 7, with an air humidifyingdevice 78, a heat exchanger 79 and a fan 80. The function of thesecomponents is analogous to the description of the components 72, 73 and74.

Since the temperature which is required at the energy supply to the airhumidifying unit is low, the inlet is connected with the outlet 42, seeFIG. 4, on the central unit, while the outlet from the air treatmentunit 28 is connected with the inlet 41. During summer operation withhigh air temperature outdoors it can be necessary instead for supplyingheat to the heat exchangers 74 and 79 to provide a cooling operation, inwhich the flow direction in the line between the air treatment unit 28and the inlet 41 of the central unit is reversed.

In the embodiment of FIG. 2 the washing machines 1 can for instance beconsidered to correspond to the units M₁ and M₃ of FIG. 1, while theheat sources 18 and 25 correspond to the units M₂ and M₄. In thisanalogy the three tanks 7, 16 and 19 of FIG. 2 corresponds to theaccumulators A₁, A₂ and A₃, while the cold water inlet 12 corresponds tothe inlet IN. The fixed connection between the heat sources 18 and 25 ofFIG. 2 corresponds in FIG. 1 to a part of the change-over device O₁,while the active connection of FIG. 2 of the washing machines 1 and thestoring tank 7 corresponds to an active part of the change-overdevice 1. In the same way the shunt valves at the inlet lines 14 and 21corresponds to the change-over device O₂ which is this analogy isactive.

The invention can be modified within the scope of the invention.

I claim:
 1. A method for the recovery of waste heat with a heat recoverysystem from a plurality of heat carrying fluids in a heat consumingplant having a plurality of waste heat sources and at least one heatconsuming unit, each of said heat carrying fluids from each of saidwaste heat sources having a different temperature, comprising the stepsof:classifying said heat carrying fluids according to the temperaturesthereof; supplying said heat carrying fluids having approximately thesame temperature to a heat exchanger for transferring the waste heatfrom said heat carrying fluids to a heat absorbing fluid associated withsaid heat exchanger; storing said heat absorbing fluid associated withsaid heat exchanger in a heat accumulator at a temperature as high aspossible and compatible with the thermodynamic characteristics of saidheat recovery system; and supplying said heat absorbing fluid from saidheat accumulator to said heat consuming unit having a temperaturerequirement compatible with the temperature of said heat absorbingfluid.
 2. The method of claim 1; wherein said heat recovery systemincludes a second heat exchanger and a second heat accumulator having asecond heat absorbing fluid, said second heat exchanger for extractingheat from said waste heat sources having temperatures higher than saidtemperature of the first-mentioned heat absorbing fluid; and furthercomprising the step of supplying said first heat absorbing fluid fromthe first-mentioned heat accumulator to said second heat accumulator. 3.The method of claim 2; wherein said step of supplying said heatabsorbing fluid comprises supplying said second heat absorbing fluid tosaid heat consuming unit.
 4. The method of claim 3; and furthercomprising the step of supplying said second heat absorbing fluid tosaid second heat exchanger before said step of supplying said secondheat absorbing fluid to said heat consuming unit.
 5. The method of claim1; wherein said heat recovery system includes a plurality of heatexchangers, each with a heat absorbing fluid and each receiving saidheat carrying fluids having approximately the same, preset temperature;and wherein the step of supplying said heat carrying fluids includessupplying each of said heat carrying fluids having approximately saidpredefined temperature to the corresponding heat exchangers.
 6. Themethod of claim 5; wherein said heat consuming plant includes aplurality of heat consuming units, each with a predefined temperaturerequirement; and wherein the step of supplying said heat absorbing fluidcomprises supplying each of said heat absorbing fluids havingapproximately said predefined temperatures to the corresponding heatconsuming unit.